Virtualization is an abstraction that decouples the physical hardware from the operating system in a data processing system to deliver greater resource utilization and flexibility. Virtualization allows multiple virtual machines with heterogeneous operating systems (e.g., Windows™, Linux™, UNIX™, etc.) and applications to run in isolation, side-by-side on the same physical host machine. A virtual machine is the representation of a physical machine by software. A virtual machine has its own set of virtual hardware (e.g., random access memory (RAM), central processing unit (CPU), network interface card (NIC), hard disks, etc.) upon which an operating system and applications are loaded. The operating system sees a consistent, normalized set of hardware regardless of the actual physical hardware components.
A conventional virtualized processing system may include a physical host machine which runs virtualization software such as a hypervisor. The hypervisor software runs on the physical host machine (e.g., a computer) and abstracts physical hardware (e.g., processors, memory, storage and networking resources, etc.) to be provisioned to one or more virtual machines.
A guest operating system (e.g., Windows™, Linux™, UNIX™, etc.) may be installed on each of the virtual machines. The virtualization software presents the physical hardware of the host machine as virtual hardware to the guest operating system and applications running in the guest operating system. A user may access the virtual machine to perform computing tasks as if it were a physical machine. Generally, the virtualization process is completely transparent to the user.
A pass-through disk is a way for virtual machines to directly access a physical disk in a virtualized computing environment. The virtualization software on the host machine provides an Application Programming Interface (API) or other tools to assign pass-through disks to the virtual machines. The user cannot, through the virtual machine, provision a pass-through disk on the host machine if necessary, and attach the pass-through disk to the virtual machine. Furthermore, the user cannot remove a provisioned pass-through disk.